In virtual networking, edge nodes handle the north-south traffic of one or more logical networks. In a multitenant datacenter, a logical network provides networking services to end machines (e.g., physical and virtual machines) of a tenant. An edge node can be a machine (physical or virtual machine) that connects a logical network to external networks (physical and/or logical networks). For providing high availability, some networks deploy a pair of active and standby edge appliances (e.g., gateways). High Availability (HA) ensures that the services provided by edge appliances are available even when a hardware or software failure renders a single appliance unavailable. One of the edges functions in active mode (i.e. actively forwards traffic and provides other logical network services), whereas the second edge node is in a standby state, waiting to take over should the active edge node fail. The active appliance maintains a heartbeat with the standby appliance and sends service updates through one or more internal interfaces (also referred to as HA interfaces).
When the active edge node is up and healthy but the two edge nodes cannot communicate with each other properly (e.g., a heartbeat is not received from the active edge node within a specified time), the standby edge node also declares itself as an active node. This scenario is known as split-brain. A split-brain can be a source of network disruption. For instance, the end virtual machines which require edge services (e.g., north bound routing, stateful services) might get the MAC address of either of the edge nodes (whichever responds first to an ARP request) since both edge nodes declared themselves as active nodes. As another example, when the edge nodes provide DHCP services, if both edge nodes are active and do not coordinate with each other, each edge node provides IP addresses to end machines that request for such independent of the other edge node. This could cause overlap in IP address assignments to the end machines (i.e., two end machines of the same network may have the same IP address). Typically, the edge nodes should be rebooted to resolve a split-brain failure.